1. Field of the Invention
The present invention relates to an image formation apparatus such as a color copying machine, a color printer, and a color facsimile that employ an image formation method such as an electrophotography method, an electrostatic recording method, and a magnetic recording method. The present invention further relates to a belt driving gear of a printing machine, and the like.
2. Description of the Related Art
Generally, an imprinting apparatus of an apparatus that requires imprinting, such as a copying machine, and a printing machine, for example, an electrostatic process copying machine, includes
one of a photo conductor drum (drum) and a middle imprint object (belt), on which a toner image is formed, the drum (or the belt, as applicable) rotating at a predetermined speed, and
a countering roller making forced contact with the drum (or the belt) and being pressed by a pressing member such as a spring. When a recording medium passes through a nip constituted by the drum (or the belt) and the countering roller, the toner image is imprinted onto the recording medium. With such a configuration, a transitional load fluctuation is generated at the drum (or the belt) due to a shock when the tip of the recording medium enters the nip and when the end of the recording medium departs from the nip because the thickness of the recording medium produces a level difference, and the rotational speed of the drum (or the belt) fluctuates.
Similar transitional load fluctuations are generated causing the rotational speed to fluctuate when the recording medium leaves conveyance rollers that convey the recording medium and when the recording medium enters fixing rollers by which the toner image is fixed on the recording medium.
The rotational speed fluctuation poses a problem in that image quality is degraded by a color shift, uneven coloring, etc. This problem is present not only with the electrostatic process copying machine, but also with other machines that imprint an image on the recording medium, such as a machine using a direct imprint method, where an image is directly imprinted on the recording medium from the photo conductor drum.
In an attempt to cope with the problem, there is an apparatus wherein an imprinting unit as a whole is made to rock. This is for reducing the amount of a shock transmitted at an image supporting object and a middle imprinting object without changing imprinting pressure, the shock being generated by the recording medium entering the imprinting apparatus (for example, Patent Reference 1). This proposed solution, however, enlarges dimensions of the apparatus because the rocking facility is provided. Furthermore, since the nip moves, an imprinting position moves, which generates a part where a period of receiving the imprinting pressure per unit length of an image is different from other parts. This causes the imprinting position to shift, posing a problem in that image concentration becomes uneven.
[Patent Reference 1] JPA 2001-265127